This invention relates generally to suppressing electromagnetic interference (EMI) within a computer system. In particular, the present invention is a peripheral component interconnect (PCI) computer system housing that includes a bulkhead gasket assembly that suppresses EMI conducted through blank and printed circuit board (PCB) bulkhead plates within the computer system housing. The PCI computer system housing employs a bulkhead plate alignment and mounting system that allows xe2x80x9chot pluggingxe2x80x9d of PCB""s within the PCI computer system housing.
As computer system frequencies and power increase, the electromagnetic energy or noise, also known as electromagnetic interference (EMI), radiating from the computer system housing increases proportionally. This EMI noise typically originates from the different components within the computer system, and can interfere with the operation of other pieces of electronic equipment associated with the computer system or in close proximity thereto. As such, computer systems typically need to comply to an electromagnetic compliance (EMC) standard which defines limits to levels of stray EMI noise. To comply with EMC standards and to protect electronic equipment from operation affecting EMI noise, the computer system components that emit EMI noise are generally placed within a shielded enclosure, such as a computer system housing. The computer system housing suppresses EMI noise emanating from computer system components by containing or otherwise diminishing stray EMI noise signals.
One type of computer system housing that attenuates EMI noise employs a PCB input/output (I/O) connection system known as the peripheral component interconnect (PCI) system. The popularity of the PCI system has grown to a point where it is the preferred I/O connection system for larger server computers as well as workstation computers. The PCI system allows one or more microprocessors (i.e., PCB""s) to be interconnected with attached external devices.
The PCI system includes a computer system housing defined by a plurality of walls. At least one of these walls is removable to provide access to an interior region of the housing to allow PCB""s to be inserted into and removed from the housing. The PCB""s are releasably connectable to a central processing unit of the computer system through a mother board, often referred to as a backplane board, as it is vertically mounted as a back wall of the computer system housing.
A wall of the computer system housing adjacent to the backplane board includes a plurality of PCI slots (i.e., between six and twelve total) which are disposed in the computer system housing to provide external access to the PCB""s mounted within the housing. Peripheral component connectors on the PCB""s extend through these PCI slots so that compatible external devices can be plugged into the PCB via the peripheral component connectors. This wall that includes the PCI slots is often referred to as the bulkhead wall of the computer system housing. In the PCI system, that portion of a PCB that includes the peripheral component connector also includes a bulkhead plate that covers the portion of the respective PCI slot not taken up by the peripheral component connector. In addition, in the PCI system, those PCI slots not currently accommodating a PCB are covered by individual blank bulkhead plates that are substantially identical to the PCB bulkhead plates and function to cover the unused PCI slots. The PCB and blank bulkhead plates are typically secured to the housing, and in particular, to the bulkhead wall via a separate screw fastener.
The walls of the PCI computer system housing generally provide some suppression of the EMI noise produced by the PCB""s mounted within the housing. However, EMI noise from the PCB""s does radiate from the PCI slots to such an extent that a typical PCI computer system housing does not meet EMC standards. To provide conduction paths to the computer system housing for EMI noise currents to meet EMC standards, bulkhead gaskets are used.
In the typical PCI system, the bulkhead gasket is placed on the interior surface of the bulkhead wall. The bulkhead gasket makes contact with the bulkhead wall and with the bulkhead plates along the two longest sides of the bulkhead plates. Typically, the bulkhead gasket is a thin (0.004xe2x80x3) stainless steel metal stamping containing a line of formed spring tabs as contact points between the bulkhead wall and the bulkhead plates. Because typical PCI slots are arranged close together on 0.80xe2x80x3 centers, there is limited space between bulkhead plates. As such, only enough room exits on the bulkhead gasket for either a single row of spring tab contacts which adjacent bulkhead plates must share, or an interlaced pattern of spring tabs which adjacent bulkhead plates do not share. With either arrangement, if adjacent bulkhead plates are misaligned relative to one another, one bulkhead plate will make little or no contact with the bulkhead gasket. Moreover, since this type of bulkhead gasket only contacts the bulkhead plates along their two longest sides, large non-contact gaps are left between the two shortest sides of the bulkhead plates and the bulkhead wall resulting in EMI noise leakage. Without contact or proper contact between the bulkhead plates and the bulkhead gasket, EMI noise will not be conducted to the computer system housing, and as such, the EMI noise will not be suppressed.
As set forth previously, each of the PCB and blank bulkhead plates are typically secured to the housing, and in particular, to the bulkhead wall via a single, separate screw fastener. Each screw passes through a slot within a mounting tab that is integral with and extends at a 90xc2x0 angle with respect to a main portion of the bulkhead plate. This screw/mounting tab slot configuration must secure and align the bulkhead plate within the PCI computer system housing. Because of this screw/slot mounting arrangement, the close center spacing of the PCI slots, and because the material thickness of the bulkhead plates is very thin (i.e., 0.030xe2x80x3), the bulkhead plates tend to misalign and overlap each other. This misalignment and overlap of the bulkhead plates results in no contact and/or improper contact between the bulkhead plates and the bulkhead gasket. As such EMI noise will not be suppressed, since the EMI noise is properly conducted to the computer system housing.
In addition, the single screw fastener bulkhead plate mounting arrangement exhibits other drawbacks. In particular, the loose screw is susceptible to being lost, or worse, being dropped into the computer system housing. As such, to insert and remove PCB""s from the typical PCI computer system housing, power to the computer system must be turned off or a repair technician risks an electrical short caused by a loose screw being dropped into the housing. Hence, the PCI computer system housing described above is not amenable to xe2x80x9clot pluggingxe2x80x9d of PCB""s (i.e., the installation and removal of PCB""s to and from the computer system housing with the power to the computer system turned on.
There is a need for an improved PCI computer system housing. In particular, there is a need for a PCI computer system housing that employs a bulkhead gasket assembly that suppresses EMI noise along the entire peripheral edges of the bulkhead plates. In addition, the PCI computer system housing should employ a bulkhead plate alignment and mounting system that properly aligns the bulkhead plates to insure adequate contact between the bulkhead plates and the bulkhead gasket to attenuate EMI noise. Moreover, the bulkhead plate alignment and mounting system should be free of loose fasteners to allow hot plugging of PCB""s.
The present invention is a computer system housing for providing an attenuating barrier for electromagnetic interference (EMI) noise. The computer system housing includes a backplane wall having a plurality of connectors for receiving PCB""s, and a bulkhead wall coupled to the backplane wall. The bulkhead wall defines a plurality of bulkhead slots through which connector receptacles of the PCB""s can extend. An EMI bulkhead gasket is positioned on the bulkhead wall. The EMI bulkhead gasket defines a plurality of gasket slots in alignment with the bulkhead slots of the bulkhead wall. Each gasket slot is defined by a first side edge, a second side edge disposed opposite to the first side edge and a bight edge connecting the first side edge to the second side edge. Each bight edge includes a plurality of bight edge spring tabs, and the first and second side edges each include a plurality of side edge spring tabs. The bight edge and side edge spring tabs are in contact with the bulkhead wall. The computer system housing also includes a conductive metal impregnated, elastomer EMI gasket positioned on a mounting flange of the bulkhead wall.
The computer system housing further includes a plurality of bulkhead plates. One of the bulkhead plates is associated with each bulkhead slot. Each bulkhead plate has a main portion that contacts the first, second and bight edges of one of the gasket slots. A mounting tab of each bulkhead plate contacts the conductive metal impregnated, elastomer EMI gasket. The mounting tab extends at substantially a 90xc2x0 angle with respect to the main portion of the bulkhead plate. The EMI bulkhead gasket and the elastomer EMI gasket conduct EMI noise from the bulkhead plates to the bulkhead wall of the computer system housing thereby suppressing the EMI noise.
The computer system housing further comprises an alignment and mounting system for securing the bulkhead plates to the bulkhead wall. The alignment and mounting system includes a bulkhead plate alignment mechanism mounted to the mounting flange of the bulkhead wall. The bulkhead plate alignment mechanism has a first alignment member adjacent to a first side edge of each of the bulkhead slots for engaging a first edge of the mounting tab of the bulkhead plates; and a second alignment member adjacent a second side edge of each of the bulkhead slots for engaging a second side edge of the mounting tab of the bulkhead plates. The first and second alignment members mount the bulkhead plates to the bulkhead wall and align the bulkhead plates with one another and with the bulkhead slots. The computer system housing further comprises a readily removable closure wall. The closure wall includes a plurality of spring fingers that form part of the bulkhead plate alignment and mounting system. Each spring finger has an elastomer element that is engageable with the mounting tabs of the bulkhead plates to secure the bulkhead plates against the EMI bulkhead gasket and the elastomer EMI gasket and between the first and second alignment members.
In this computer system housing of the present invention, the EMI bulkhead gasket and the elastomer EMI gasket suppress EMI noise along the entire peripheral edges of the bulkhead plates. In addition, the bulkhead plate alignment and mounting system properly aligns the bulkhead plates to insure adequate contact between the bulkhead plates and the bulkhead gasket to attenuate EMI noise. Moreover, the bulkhead plate alignment and mounting system does not employ separate fasteners that can be easily dropped within the computer system housing. As such, the bulkhead plate alignment and mounting system allows xe2x80x9chot pluggingxe2x80x9d of PCB""s.